biological clock

biological

2. a medicinal preparation made from living organisms and their products, such as a serum or vaccine.

biological clock the physiologic mechanism that governs the rhythmic occurrence of certain biochemical, physiologic, and behavioral phenomena in living organisms. See also biological rhythms.

biological clock

n.

1. An internal mechanism in organisms that controls the periodicity of various functions or activities, such as metabolic changes, sleep cycles, or photosynthesis.

2.

a. The time period during which a person who desires to have a biological child, especially a woman approaching the decline of reproductive capability, is still able to do so.

b. The capacity to be fertile, especially in such a woman: She was eager to have a child before her biological clock stopped working.

Physiology An organism’s internal timer that sets biological rhythms—e.g., metabolism, sleep-wake cycles, and photosynthesisVox populi As currently used, that which ticks away the time left for a woman to have babies, ideally before age 40

biological clock

or

internal clock

an internal mechanism (as yet poorly understood) by which many plants and animals keep a sense of time, making possible a rhythmic pattern of behavour. Many organisms have such ‘clocks’ producing activity cycles of approximately 24 hours (CIRCADIAN RHYTHMS) which, however, can be affected by external influences that ‘set’ the clock (entrainment). An individual's clock can be re-entrained if placed in a new time zone, but after rapid, long-distance travel the process can take several cycles, creating ‘jet-lag’ until internal and external rhythms are synchronized. Biological clocks affect not only whole organism activities (e.g. sleeping) but also cellular patterns of activity (e.g. varying METABOLIC RATES). See also DIURNAL RHYTHM.

Biological clock

A synonym for the body's circadian rhythm, the natural biological variations that occur over the course of a day.

biological

2. a medicinal preparation made from living organisms and their products; these include serums, vaccines, etc.

biological clock

the physiological mechanisms which govern the rhythmic occurrence of certain biochemical, physiological and behavioral phenomena in living organisms. See also biological rhythm.

biological control

control of a parasite by making use of its natural enemies, especially other pests. The target may also be a vector or a reservoir for infection.

biological data

usually comprise a list of vital statistics about an animal or plant species, recording such things as preferred growth medium, temperature and humidity and details of the internal milieu including blood pH, normal blood electrolytes and the like.

biological environment

includes the influence of all biological factors such as warmth, moisture and humidity, but also the plant ecosystem in which the animal lives and the associated populations of vertebrates and invertebrates that may compete for food and space, and may also act as reservoirs for infectious diseases.

biological filters

are used for the treatment of sewage effluent. They comprise a column of stones or plastic pieces which become covered with bacteria which degrade the organic matter in the effluent.

biological significance

is an estimate of the biological importance of a statistical or apparent causal association between two variables, e.g. feed supply and the occurrence of bovine acetonemia. The estimation takes into account the possible biological relationship between the two; an estimate of statistical significance would take only the mathematical relationship into account.

biological value

relationship between the amount of nutrient absorbed and the amount utilized by the body. Expressed as a percentage. Called also BV.

The problem with this hypothesis was shown by Johnson and Rokas' study of the effect of changing codon usage on the simple biological clock found in single-celled cyanobacteria (blue-green algae) and a similar study of the more complex biological clock found in bread mold performed by a team led by Yi Liu that were published together.

Dr Chris Ford, of St Michael's Hospital, Bristol, which took part in the study, said: "It tells us that to some degree men as well as women have a biological clock that starts ticking as they get into their thirties.

Each insidious tick is telling me that time is wasting and that if I want to have a child, I'd better get a move on "Men don't have biological clocks," a friend snapped at me in response to my worries.

The discoveries raise the possibility that many other organisms, including humans, may have multiple timers, says Charlotte Helfrich-Forster, who studies biological clocks at the University of Wurzburg in Germany.

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